1. Field of the Invention
This invention relates generally to subsea connections for marine risers from a subsea well.
2. Description of the Prior Art (Prior Art Statement)
The following statement is intended to be a Prior Art Statement in compliance with the guidance and requirements of 37 C.F.R. 1.56, 1.97 and 1.98.
U.S. Pat. No. 3,559,410 to Blenkarn et al. discloses a tension leg for anchoring a tension leg platform, said tension leg having a rigid connection of the riser at the ocean floor, with a ring type structure (see 52 and 54 of FIG. 3) for limiting lateral movement of the riser and thereby limiting stresses in the riser at the ocean floor connection. Blenkarn et al. does not disclose a rigid mounting of the riser downhole within the casing below the ocean floor and the use of the upper end of the casing as a means for allowing limited lateral deflection of the riser at the ocean floor.
U.S. Pat. Nos. 3,142,343 and 3,142,344, both to Otteman et al., each disclose a tiltable collar 27 located above an upper end 36 of a casing 26 within which a riser pipe 34 is disposed. The riser 34 contacts upper end 36 of casing 26 and contacts the tiltable collar 27 to limit lateral movement of riser 34 and thereby limit stresses within the riser. Also, FIG. 2 of Pat. No. 3,142,344 shows a rigid collar 27a having a flared lip 29. Neither of those references discloses a rigid mounting of the riser downhole within the casing below the ocean floor, nor do they disclose the use of the upper end of the casing alone for limiting lateral deflection of the riser at the ocean floor, with the riser being free of contact with any other structure between the contact with the upper end 36 of casing 26 and the contact with the floating vessel.
U.S. Pat. No. 3,670,507 to Mott et al., No. 3,618,679 to Crooke, No. 3,556,210 to Johnson, No. 3,496,898 to Morgan, No. 3,403,728 to Richardson et al., No. 3,189,372 to Johnson and No. 3,017,934 to Rhodes et al. also relate to the reduction of stresses in marine risers and the like.
It is seen from these references that the prior art has recognized the need for a connection between the riser pipe and the subsea well which will limit the stresses to which the riser is subjected when the floating structure to which the riser is attached is tossed about by wind and waves. The present invention provides an improved and simplified connection which accomplishes this result.